An Experiment on Breeding Wild Pairs of Gammarus cheureuxi at a High Temperature, with an account of Two New Recessive Types of Red Eye

On each of two former occasions when specimens of Gammarus chevreuxi Sexton have been brought from the wild into an incubator and kept at 21° C. or more, red-eyed recessive types have been reared among the F2 progeny (4, pp. 190 and 194). In November, 1930, an opportunity occurred for making further tests on this point. Twenty-three wild pairs, taken in Chelson Meadows on November 19, were placed on the following day in the incubator, the temperature of which at first averaged between 21° and 22° C, but was raised after a few days to an average of between 22° and 24° C. The young which were extruded from eggs laid in the wild were discarded. Those of subsequent broods were reared with a view to obtaining as many F2 families in each stock as would give a reasonable opportunity for segregating recessive characters to appear. The F2 young were examined for recognisable variations that might indicate the presence of a recessive character.